Scala练习题

1、定义一个高阶函数，按照指定的规则对集合里面的每个元素进行操作
比如: Array(“hh”,“red”,“java”,“hadoop”)
规则: 对集合中每个元素进行操作，得到集合每个元素的长度

package lj

object aaa {
    def main(args: Array[String]): Unit = {
      val list = Array("spark", "hello", "java", "hadoop")
      val fun = (s: String) => {
        s.length
      }
      println(doSome(list, fun))
      println(doSome(list, (s: String) => {
        s.length
      }))
      println(doSome(list,(s)=>s.length))
      println(doSome(list,s=>s.length))
      println(doSome(list,_.length))
    }

    def doSome(list: Array[String], fun: (String) => Int) = {
      val res = for (elem <- list) yield {
        fun(elem)
      }
      res.toList
    }
}

运行结果：

2、定义一个高阶函数，对数据中的元素按照指定的规则进行过滤
比如: Array(1,4,7,9,10,6,8,99,88,66)
规则: 只保留偶数数据

package lj

object aaa {
    def main(args: Array[String]): Unit = {
      val list = Array(1,4,7,9,10,6,8,99,88,66)
      println(filter(list,(_%2==0)))
    }

    def filter(list: Array[Int],fun:(Int)=>Boolean) = {
      //用fun做守卫,过滤
      val res = for (elem <- list if (fun(elem))) yield {
        elem
      }
      res.toList
    }
  }

运行结果:

3、对数据中的元素按照指定规则进行分组
比如:Array(“zhangsan shenzhen man”,“lisi beijing woman”,“zhaoliu beijing man”)
规则: 按照地址进行分组

object Test03 {
  def main(args: Array[String]): Unit = {
    val list = Array("zhangsan shenzhen man","lisi beijing woman","zhaoliu beijing man")
    println(group(list,_.split(" ")(2)))
  }

  def group(list:Array[String],fun:(String)=>String) = {
    val map = new util.HashMap[String,util.ArrayList[String]]()
    for (elem <- list) {
      val key = fun(elem)
      if(map.containsKey(key)){
        map.get(key).add(elem)
      }else{
        val value = new util.ArrayList[String]()
        value.add(elem)
        map.put(key,value)
      }
    }
    map
  }
}

4、根据指定规则对数组所有元素聚合
比如:Array(10,4,6,10,2)
规则: 求和/求乘积

package lj

object aaa {
    def main(args: Array[String]): Unit = {
      val list = Array(10,4,6,10,2)
      println(poly(list,_+_))
    }

    def poly(list:Array[Int],fun:(Int,Int)=>Int) = {
      var res = list(0)
      for (i<-1 until list.size) res = fun(res,list(i))
      res
    }
}

运行结果：